Automotive electrochromic minor reflective element cell assemblies typically include a front substrate and a rear substrate and an electrochromic medium sandwiched therebetween and contained within an interpane cavity. The substrates are shaped as desired by the automobile manufacturer for a particular mirror design or application. For example, an interior rearview mirror reflective element may have substrates that are generally oval or trapezoidal in shape and are formed to be approximately 20-26 cm long and 5-8 cm tall or wide. Exterior minor reflective element assemblies are shaped differently and may have sharper radii at the corners and may be flat or convex or aspheric, depending on the particular application. The size of the substrates for the exterior reflective element assemblies may vary from about 7 cm by 7 cm to about 10 cm by 18 cm or larger.
During manufacture and assembly of the reflective cell element assembly, the respective front and rear substrates are often cut or broken out as cut shapes from larger flat or curved lites, typically glass sheets or lites. The individual front and rear cut shapes or substrates are cleaned and then coated with a conductive or semiconductive coating or coatings that are reflective or transparent. After they are coated, an uncured adhesive material, typically an uncured epoxy material (often containing spacer beads, such as glass beads or the like), is applied around the perimeter of one of the cut shapes or substrates, and the other cut shape or substrate is superimposed thereupon and spaced apart from the first cut shape by the applied perimeter material. The uncured adhesive material is then cured, such as by heating, to adhere the shapes or substrates together and to space the substrates apart a desired amount to define an appropriate interpane cavity spacing. The substrates, so adhered together and interspaced apart, form an empty cell with an interpane cavity between the substrates and bounded by the perimeter seal. Next, an electrolyte or monomer composition is filled into the cavity via an aperture (commonly known as a fill port or plug hole) provided in the perimeter material or seal, such as via a vacuum fill process. However, until such time as the interpane cavity is formed by the juxtapositioning and superimposing of the respective front and rear shapes or substrates of the electrochromic cell, dirt or glass chips or dust or skin flakes or other debris or contaminants or the like may fall onto or contact the pristine surface of any one of the substrates (the pristine surfaces are the opposing surfaces of the front and rear substrates that oppose one another when the substrates are held together and that are contacted by the electrolyte or monomer composition or electrochromic medium in the interpane cavity). Such contaminants (whether contacting the surfaces before or after coating) may interfere with the coloration/bleach mechanism and/or the coating durability/adhesion (such that voids may exist in the coating due to glass chips or the like), as well as affect the perimeter seal adhesion, and thus often result in a flawed cell exhibiting cosmetic defects that is often discarded or scrapped.
In order for the completed mirror reflective element assembly or cell to avoid such flaws, the pristine surfaces (that will oppose one another when the substrates are adhered together and that have the semiconductive or conductive layers applied thereto) of the substrates preferably must be kept clean and untouched throughout the coating, conveying, adhering and assembly processes. Difficulties in keeping the surfaces pristine are often encountered because the individual cut shape substrates are often handled and conveyed as they are moved from one process or station to the next. Often, the individual cut shape substrates are cleaned, such as via an ultrasonic cleaner or scrubber to remove any such debris or the like. However, the individual cut shape substrates may be conveyed along a conveyor and held down via rollers during the scrubbing process, where the rollers often encroach and so touch the pristine surface of the substrate that will be the inner surface of the cavity. If any marks or debris are left by the rollers, they may be visible in the finished product and may result in the cell being scrapped.
It is also known to provide display windows in the reflective coating or layer of a reflective element assembly, such that a display device or illumination source may be viewable through the display window. Typically, for fourth surface reflective element assemblies (where the metallic reflective coating or layer is applied to the fourth or rear surface of the reflective element assembly), such display windows may be formed in the reflective coating of the substrate via laser ablating or etching or sand blasting the reflective coating from the window area of the fourth surface (i.e., the rear surface of the rear substrate) after the reflective mirror coating (typically a silver mirror reflector layer overcoated with a copper layer and protected by a paint overcoat) is applied over substantially the entire fourth surface. The reflective coating is removed from the desired window area such that the glass or substrate surface is exposed on the fourth surface in the window area.
However, such an approach does not readily apply to forming windows through the metallic reflective coating of third surface reflective element assemblies (i.e., a reflective element assembly that has the metallic reflective coating on the third surface (the front surface of the rear substrate) of the reflective element assembly). In order to properly darken or color the electrochromic medium disposed between the substrates, the opposed surfaces of the substrates (the front surface of the rear substrate and the rear surface of the front substrate) are coated substantially over their entire surfaces with a conductive coating. Typically, the second surface (the rear surface of the front substrate) is coated with a transparent electrically conductive coating, such as an indium tin oxide (ITO), while the third surface (the front surface of the rear substrate) is coated with a transparent electrically conductive coating, and is further coated with a metallic reflective conductive coating over the transparent coating. When it is desired to form a window in the metallic reflective conductive coating on the third surface, it is desirable that the window on the third surface still have the transparent electrically conductive coating over its surface area, in order to provide for appropriate darkening or coloring of the electrochromic medium at the window area. If the transparent electrically conductive coating is also removed from the third surface in the window area, the electrochromic medium may not darken or color uniformly across the reflective element assembly, particularly in the window area versus the rest of the reflective element assembly. However, it may be difficult to laser ablate or etch only the metallic reflective coating from the third surface while leaving the transparent electrically conductive coating intact on the surface of the substrate at the window area. Such precise control of the depth of the ablation or etching may be difficult to achieve.
Therefore, there is a need in the art for an improved process for manufacturing electro-optic minor reflective element assemblies, such as electrochromic mirror reflective element assemblies, that overcomes the shortcomings of the prior art.